1. Field of the Invention:
This invention relates to devices and techniques for sealing cylindrical members to circumscribing conduits. More specifically, the present invention relates to a well packer for sealing a pipe string to a surrounding well conduit, such as is provided by the casing or a well liner, and is suitable for use in high temperature applications.
2. Description of the Prior Art:
Well packers and other downhole equipment are often exposed to high temperatures. In particular, certain secondary recovery techniques for producing hydrocarbons include thermal recovery operations. Such operations include fire flooding and steam injection. In a fire flooding operation, oil said about the periphery of a high viscosity oil formation is ignited and the fire is maintained by the injection of air through wells about the formation horizon. As the combustion front advances through the formation, the oil decreases in viscosity and increases in mobility, moving toward one or more producing wells communicating with the interior of the formation.
Steam injection techniques include the injection of steam into wells to reduce the viscosity of the formation oil, so that the oil can be removed by a producing well. Alternately, the steam can be circulated down a well through which the reduced viscosity oil is produced, with the oil being isolated from the steam within the well bore.
Where thermal operations of the above types are being carried out, downhole equipment is subjected to unusual stresses caused by variations in the length of the equipment, particularly the tubing string, due to the wide ranging temperature changes which must be accomodated. U.S. Pat. No. 3,391,742 discloses a mechanically set, retrievable well packer, adapted for use in high temperature well operations. After the packer is set, the tubing string used in running the packer into position can be moved longitudinally, relative to the outer packer assembly, which is sealed and anchored to the surrounding well conduit, without unseating the packer. A dual mandrel assembly provides the capability of circulating steam while producing hydrocarbons through the packer.
U.S. Pat. No. 4,375,240 shows a hydraulically set, retrievable well packer, adapted for thermal recovery operations. The sealing members utilized in the packer are constructed of a material which permits the mandrel to remain sealed to the well conduit in the presence of high temperatures. The packer can be released by straight longitudinal movement of the mandrel, relative to the outer packer assembly.
Even though the above packer designs perform satisfactorily in thermal recovery operations, there exists a need for a thermal packer of simplified design and lower overall manufacturing costs. There exists a need for such a packer with fewer moving parts and simpler operation for improved reliability. There exists a need for such a tool which can be set by immediate rotation of the running string without the need for longitudinal movement to unjay a latch mechanism. There also exists a need for such a tool with an improved release mechanism to facilitate retrieving the device from the well bore.
These and other objects are accomplished as described in the specification which follows.